Method and apparatus for testing cables

ABSTRACT

The integrity, connection and location of cable wire termination extending between two different points is checked for shorts between wires and open wires. The actual remote termination plug configuration can be mapped from testing end to determine remote plug wiring. The actual location of the remote terminated end is identified either by a visual indicator, a electronically recorded message made by operator at time of cable termination, or both.

FIELD OF THE INVENTION

[0001] This invention relates to methods and apparatus for testing cables used in telephone, communication, video cables, and computer networks for identification of cable location and for a number of wire faults, such as (1) shorts between wires (2) open wires (3) improper connection of wires to terminating plugs, and (4) reversed wired terminating plugs.

BACKGROUND OF THE INVENTION

[0002] During the installation of and interconnection of various equipment in telephone, video, and computer networks, it is necessary to make frequent wiring checks as to the integrity of connections made by means of exchange cable which is utilized to interconnect the various equipment. In many instances cable connectors are installed at the site of use using hand tools and special connectors. It is necessary that the cable be checked for proper connection of the plug terminals and identified as to its remote location when connected to the computer hub, telephone KSU (Key Switching Unit), or video distribution box.

[0003] A number of test facilities have been developed for making a number of checks of cable with connectors on ends so as to ascertain shorts, continuity and proper wire interconnection. One such test facilities is shown in U.S. Pat. No. 3,492,571 to D. A. Desler assigned to the Western Electric Co., Inc., where a multi-conductor cable having plugs at opposite ends is checked for shorts, opens and wires that are misconnected or cross-connected between terminals at the respective plug ends of the cable. This test facility includes means for sequentially applying test pulses to terminals at one plug end and sensing the receipt of the signals at the second plug end. The received signals are then compared with signals generated by a reference program circuit. The signals from the plug end of the wire and the reference circuit are applied to a comparison circuit to determine correctness, and if the signals do not properly compare then error signals are generated. The error signals are utilized to operate visual displays that provide information as to the faulty wires and the type of error determined by the comparison circuit.

[0004] There is a need for a lightweight, portable test unit for checking cables and cable wiring on a users site that can be transported, set up and run by a single operator. In each site or office such a test unit should be able to test for shorts between wires, open wires and misconnected or cross-connected wires, and this test unit should also have the capability of identifying the location of the remote terminated end of the cable under test. In addition, the test unit must be easy to use and user friendly.

BRIEF SUMMARY OF THE INVENTION

[0005] This invention contemplates, among other things, methods and apparatus for conducting a number of tests on cables such as improper wire or cross wire connections, open wire conditions, actual remote plug wiring, and remote plug location.

[0006] More particularly, an operator determines a name for the location of the end of a cable to be terminated. This name could be as simple as a room number or as complex as a floor number, company name, office area, and desk number. This name could then be recorded onto a sheet of paper next to a load number (i.e. Load1=3rd floor, office 3, desk 2), or the load could be plugged into the test unit and the location name could be recorded into the memory of the test unit using speech (i.e. record button is pressed and operator says “Third floor, office three, desk two”). The associated load is then connected to the cable at that location. This process is repeated for a number of loads.

[0007] The operator then proceeds to the originating point of the cables to be tested, usually a computer hub, video cable box, or Telephone Key Switching Unit (KSU). Cable integrity should be tested first to insure other readings are not corrupted by a cable fault. The test unit is then placed into the mapping mode and each cable is tested wire by wire for proper termination, no open wires, and no shorted wires. This process is repeated until the integrity of each cable has been verified.

[0008] The operator then places the test unit into the locating mode and connects a cable to be identified to the test unit.

[0009] During this test, the operator presses play and the test unit plays the previous recorded message associated with the load on the end of the cable now connected to the test unit. Or the operator checks the light indicating the load number and checks his written log to see what is written by that load number to determine the location of the remote end of the cable. Both methods are simple and user friendly requiring no deep understanding of electronics or transmission technology.

[0010] In the situation where a faulty wire is detected and the fault is due to an open or shorted condition, the location feature may still function provided the short or open is not on the pair being used to identify the cable location. The cable should then be repaired and tested again. In the case where a fault is on the pair being used to identify the cable, the process of elimination can be used to identify all good cables first, then proceed to repair the cables that were not identifiable.

[0011] Other features and advantages of the invention will be apparent upon consideration of the following detailed description and appended claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a diagram of a typical office with a group of cables originating at a server computer hub and each cable branching to a different office location;

[0013]FIG. 2 is a schematic of a test unit with interconnecting eight (8) wire cable terminated with a test unit load at a remote location showing how pairs are generated in the load for correct, reversed, and incorrect wiring;

[0014]FIG. 3 is a schematic circuit and block diagram of the principal electrical components contained in a test unit for conducting a number of tests on cable connected with a test unit load;

[0015]FIG. 4 is a schematic showing circuit connections utilized to conduct short and open wiring tests on the cables, and used to map remote plug connections on a cable without shorts or opens; and

[0016]FIG. 5 is a schematic circuit showing the principal electrical components used in the location test for cables terminated with a test unit load containing a unique resistor that identifies that load.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The following is a detailed description and explanation of the preferred embodiments of the method and apparatus of the invention.

[0018] The test unit and loads forming the subject matter of the present application is designed to test cables of two or more wires with one of these possibly being the shield in a coaxial cable. First ends of the cables are usually connected to central source from which signals originate at a factory or office, and then the cables are transported to remote locations where second ends of the cables are to be installed on computer ports, modems, telephones, or video equipment to name only a few. For purpose of illustrating the operating principles of the test set, the present description will be confined to a consideration of the testing of cables consisting of four pairs of wires originating at a server computer hub and ending at different remote computer locations. The test unit allows various tests to be conducted at either end of the cable provided a test unit load has been installed on the opposite end of the cable. It is customary, but not required, that the test unit is used at the server ends of the cables since the location would always indicate the server end if used otherwise. More particularly, the test unit is designed to test the cable wires with attached test unit loads for (1) shorts between individual cable wires, (2) shorts between center conductor and shield if cable is coaxial type, (3) opens in the individual cable wires, (4) mapping of remote plug pin connection and (5) location of the remote end of the cable.

[0019] Referring to FIG. 1, the cables to be tested are designated by the reference numerals 10 through 17, which are connected at first ends to server hub 21, which in turn is being driven by server computer 20. It should be noted that during the testing of the wires of cable 10, the plugs on cables 11 through 16 are not connected to the test unit but are connected to test unit loads. The remote plugs must be electrically connected to test unit loads and not to other equipment in order to test that cable. The first ends of the cables are, more specifically, connected to the test unit one at a time and using the remote test unit load, wires in each cable are tested sequentially.

[0020] Referring to FIG. 2 of the drawings, the load contains an RJ type plug (201) and a coaxial type plug (203). Any RJ type connector of 8 wires or less will fit into opening (201) and lock into catch (204), The cable wires will make contact to spring type contacts (202). The coaxial plug (203) provides connection to video and coaxial cables.

[0021] Referring to FIG. 3 of the drawing, the load contains a resistor (302) used to identify that particular load and various diodes (303 through 306) used to identify wire pairs. Diode (306) connects to RJ Plug (300) pins 1 and 8. Diode (305) connects to RJ Plug (300) pins 2 and 7. Diode (304) connects to RJ Plug (300) pins 3 and 6. Diode (303) connects to RJ Plug (300) pins 4 and 5. Coaxial plug (301) is also connected to pins 4 and 5 of the RJ plug.

[0022]FIG. 4 of the drawings, is a block diagram that describes the tester (22). FIG. 5 shows the schematic for the connection of the electronic parts contained in each block shown in FIG. 4. Each section in dashed lines in FIG. 5 represents a block in FIG. 4. Referring to FIG. 5, when the pushbutton (912) in section 1 is pressed, the capacitor (933) is charged to the battery voltage through one pole of the switch (912). Inverter (931) in section 3 has very high input impedance to prevent capacitor (931) from discharging. The discharge time is therefore set by either resistor (925) or resistor (924) in section 2, depending on the switch position of the 4 pole switch (920 to 923) in section 2. This discharge time determines the turn off time used to shut off the tester when it is left idle. This function is represented in FIG. 4, by Block 3, “B+TIMER CIRCUIT”.

[0023] After power is applied to all circuits, the resistor (940) and Zener diode (944) keep the transistor (946) switched on. If the battery voltage (910) falls below the Zener diode (944) voltage, transistor (946) will switch off allowing current to flow through resistor (941) and turn transistor (945) on. Current will then flow through resistor (942) and light emitting diode (943) indicating a low battery voltage condition exist. This function is represented in FIG. 4 by Block 4.

[0024] After turning on the tester (22), Repeated pressing of the ON-OFF switch (912) in Section 1, will reset the turn off time and bring the input of inverter (53) in Section 5 to ground by shorting resistor (913) on that input to ground. This action creates a single pulse that is filtered by resistor (55) and Capacitor (54) to eliminate any switch noise. In FIG. 4, this action is represented by block 5, “SINGLE PULSE GENERATOR”.

[0025] In addition, closure of pushbutton (912) initiates the next pair test by stepping the ring counter (60) to the next position in a ring of 8 possible positions and activates one electronic switch in the switch group (100, 102, 104, 106, 108, 110, 112, and 114). This function is represented by Block 6 in FIG. 4.

[0026] When a switch in Section 10 is activated it switches the output of a continuously running oscillator circuit, Section 8, to impress an AC square wave on one of the cable wires in the RJ type plug (136). This action also activates both diodes in the pairs of light emitting diodes that form the group (116 to 131). The AC square wave is sent to the load (200) by the connected cable under test (10 through 17), passes through one of the load diodes (303 through 306), and returns to the tester through the wire connected to the other end of that load diode to another pin on the RJ plug (136) Since the load diode blocks current in one direction, only one of the diodes in the pair connected to the return pin of the RJ plug (136) will be activated. The color of the light emitting diode that is activated on the return pin indicates if the cable has been wired straight through or cross pinned. These functions are represented in FIG. 4. by Blocks 8 “SQUARE WAVE GENERATOR”, 10 “ELECTRONIC SWITCHES”, 11 “INPUT OUTPUT, SHORT, OPEN, AND LOCATION INDICATORS”, and 200 “REMOTE LOAD”.

[0027] OPEN: If a cable pair under test is open, then only the transmitting pair of light emitting diodes will activate. Only two light emitting diodes on indicates an open.

[0028] SHORTED: If a cable pair is shorted then the blocking diode in the load is eliminated and both light emitting diodes on the return pin will activate with the transmitting pair. Four or more light emitting diodes on indicates shorts.

[0029] GOOD PAIR: When three light emitting diodes activate the pair under test is good.

[0030] When switch (920 to 923) is placed in the “MAP” mode, the resistance in the load is placed on the input of the load identifier circuit (90). This circuit lights one of the light emitting diodes in the group (116 through 131) according to the load resistance (302) value. In cross pinned cables the diode in the load (303) that is in parallel with the load resistor (302) will become forward biased and change the load resistance value. In cross pinned cables the switch (70,71) is used to reverse the wires of a cross pinned cable to make it into a straight through connection to the load.

[0031] This function is performed by Block 9 and Block 7 in FIG. 14.

[0032] To maintain accuracy as the battery voltage decreases the Load Identifier Circuit (90) is powered by a voltage regulator circuit (353). This function is performed by Block 13 in FIG. 4.

[0033] When the tester (22) is in the “MAP” mode the output from the load identifier circuit (90) is used to activate one of the memory addresses M1 through M7 in the speech record and playback circuit (270). If record/playback switch (252) is in the record position, a spoken message corresponding to the attached load will be placed into that memory address when the enable button (255) is pressed. If record/playback switch (252) is in the playback position, the prerecorded message corresponding to the attached load (200) will be played on the speaker (253) when the enable button (255) is pressed. In this manner a prerecorded message can be entered into the tester before the remote load (200) is placed on the cable in a remote location. The tester can then sense the load resistor (302) from the other end of the terminated cable and play back the message that corresponds to that load (200). In this way each load can have a unique message in any language prerecorded into the tester. This message is capable of being modified by the user each time the enable switch is pressed if the record and playback switch (252) is in the record position. Busy lights (258, 260) are provide for both the record and playback mode. This function is represented in FIG. 4 by Block 12.

[0034] Though the afore-described applications of the invention relate to a cable that has connectors at one or both ends, it is to be understood that the invention has applicable uses in the testing of cables that do not have connectors at either end. For example, the described test facility may be used to test the integrity of any cable at a cable manufacturing installation or the test facility may be used to test cable extending between any two electrical devices.

[0035] Although embodiments of the invention have been shown and described, it is to be understood that various modifications and rearrangements of parts, components, and method steps, can be made by those skilled in the art without departing from the novel spirit and scope of this invention. 

What is claimed is:
 1. A test unit and associated loads used for detecting open, shorted, or improper wire connections of a multiple wire cable as well as location of the remote end of the cable under test by: attaching a unique load which terminates cable in such a manner as to create wire pairs capable of passing current in only one direction; wires are tested one at a time with a positive and negative alternating voltage and direction of current loop through load plus return wire path is used to indicate remote plug wiring; each load has an electronic identification associated with one pair of wires, by unique resistance value in parallel with that pairs non-linear element; after reading load resistance value, test unit displays unique number for that load; if load resistance is too great test unit indicates open pair; if either wire in pair is shorted to another wire test unit indicates undesired shorts.
 2. A test unit with loads as defined in pre-claim 1, which comprises: a method to record speech in the test unit when load is connected directly to test unit before being applied to cable; a device to associate recorded speech with its corresponding load; upon reading load resistance value from unloaded end of cable, test unit identifies position of remote termination by playing message recorded in test unit by user when load was installed.
 3. A method of determining a cables remote location by use of prerecorded speech that: identifies the load on the remote end of the cable; can be changed to match the position of the load when it is moved.
 4. A system for mapping a cables remote plug wiring by using positive and negative voltages impressed upon a sending wire and a non-linear termination on the remote plug to create a return wire path that; will create a current when positive voltage is applied and plug is connected straight through; will create a current when negative voltage is applied and plug is connected in reverse direction.
 5. A system to determine a cables remote location by using a group of resistance values greater than what would exist in normal cable wiring and less than the resistance of an open pair by: separating values placed in each load with enough resistance to make normal cable resistance and any other stray resistance insignificant in accurate value determination; and spacing the values in the group with a large enough resistance to make a unique determination easily readable. 